Three-Phase Circuit Power Quiz

In a three-phase circuit, the true power (watts) is found by _____.

• multiplying line voltage by line current

• multiplying apparent power by the power factor

• dividing power factor by the apparent power

• multiplying phase voltage by phase current

In calculating power in a three-phase circuit, the phase values of voltage and current are multiplied by _____.

• three

• four

• five

• six

When calculating the power of a pure resistive load, the voltage and current are in phase with each other and the power factor is _____.

• one

• two

• three

• four

If a three-phase load is a pure reactive load, then the power calculated has units of _____.

• VA

• W

• VARs

A delta-connected three-phase alternator is driving a wye-connected resistive load. The alternator output voltage is 480 V. The load resistors are 12 Ω each. What is the phase current in the alternator?

• 13.33 A

• 40 A

• 39.28 A

• 23.09 A

An open delta transformer is constructed from two 75KVA transformers. What is the output power of this transformer?

• 132.9 KVA

• 176.9 KVA

• 150 KVA

• 129.9 KVA

The alternator must supply the _____ for each of the loads.

• capacitance

• line current

• inductance

• voltage

A wye-connected secondary has a phase voltage of 277.14 V. What is the line voltage?

• 160 V

• 277.14 V

• 480 V

• 554.28 V

A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. How much is the secondary phase current?

• 1.6 A

• 2.54 A

• 3.2 A

• 4.8 A

A wye-delta transformer has a turns ratio of 2:1. It has a secondary line voltage of 480 V. The secondary is connected to a wye-connected three-phase resistive load of 50 Ω in each phase. How much is the primary line current?

• 1.6 A

• 1.924 A

• 2.77 A

• 3.2 A